Nearly 20 years after murine embryonic stem cells (mESC) were isolated, the first report of the derivation of human embryonic stem cells (hESCs) in 1998 spawned the field of hESC research. Although this field is only in its infancy, hESCs have already been shown to be capable of long-term self-renewal in culture and have remarkable potential to develop into many different cell types in the body (known as pluripotency). They therefore represent a theoretically inexhaustible source of precursor cells to treat degenerative, malignant, or genetic diseases, or injury due to inflammation, infection, and trauma. This pluripotent cell has been hailed as a possible means for treating diabetes, Parkinson's disease, Alzheimer's, spinal cord injury, heart failure, and bone marrow failure. Meanwhile, hESCs are an invaluable research tool to study human development, both normal and abnormal, and can serve as a platform to develop and test new drugs. Our long-term goal is to define new conditions and molecular programs that govern fate decisions of hESCs. The knowledge is essential if we are ultimately to use these cells for therapy. The current understanding of hESC long-term self-renewal or lineage-specific differentiation is extremely rudimentary. As an attempt to address these questions, we screened a small collection of pharmacological inhibitors and identified a protein Ser-Thr kinase, as a key regulatory molecule that controls the undifferentiated growth of hESCs. This pilot study provided proof-of-concept for applying large-scale library screening to the study of hESCs. Accordingly, we will develop cell-based high-throughput assays by establishing hESCs containing enhanced green fluorescence protein (EGFP) or luciferase reporters for pluripotentcy or for directed differentiation. The results from the study will set the stage for large-scale library-screening efforts for searching molecules that influence the fate decisions of hESCs. Therefore, we expect that these assays will provide new tools for the scientific community to study the molecular mechanisms underlying hESC fate determination and may contribute to effective strategies for tissue repair and regeneration. Human embryonic stem cells (hESCs) hold considerable promise for understanding early human development and for finding and testing new drugs for a vast number of conditions, including cardiovascular diseases, neurodegenerative processes and diabetes. To realize the therapeutic potential of hESCs, we present experiments to establish high throughput assays for determining how, at the molecular level, these cells self-renew in culture and differentiate into a specific type of cells in the body. These assays may also facilitate production of sufficient differentiated cells to allow us to assess the therapeutic potential of hESCs in preclinical models of diseases, and to offer platforms for drug development.